Originally published on hexisteme notes.
I built a publish-blocking gate for a monetization agent. A draft gets registered, then judged, and the verdict comes back one of three ways: PASS, BLOCK, or AWAIT_HUMAN. Five machine gates run in sequence before a human ever sees the draft — check_warrant_gate, check_numeral_gate, check_expression_gate, check_disclosure_gate, check_revenue_axis_gate — living in agent_blog/gates/, dispatched from a tuple in verdict.py. Every gate had a unit test. Every unit test was green.
Then I told a verification agent to stop reading the tests and go break the thing for real. Four rounds later: 19 blocking defects found. Three of them had been sitting directly underneath tests that had never once gone red.
That gap is the subject of this post, because it isn't specific to this codebase. Green unit tests prove behavior — what a function does when you call it. They don't prove reachability — whether production ever calls it, whether the value survives the trip between call sites, or whether a failure gets reported as the thing it actually was. Those are three separate claims, and each one needs its own kind of evidence.
The measurement that makes the point concrete
